Production of photographic emulsions



Patented Get. 24,

red; Pankhutst, es" Morris Smith 1, more; England; 'afssignorS to 11mmLimited?" anrjitish co ally Application Marchfilk n'iejreap Britai'n'October so, 1944 i g gplaims', (01;:95zr7 This mventionrelates totheproduction'ot N silver"halide-photographic emulsionsw- Ithas beendiscovered. that when there added to an emulsion of silver-' halideinigelatinfait alow pH value, -a-su'lphonic acidcontaining a highlyhydrophobic radicle-inthe-ani'on, elf-coma plex is formed between thegelatin andsulph'onic acid and this separates out carrying-thesilvenhalide with it. It -has further been discovered that complexesthusformed are readil'y 'dis'pe-rsible in organic.solvents,- e; g:methyl alcoholf The term -sulphonic acid is to beunderstood to includesulphonates. Accordingto thisinvention, therefore, photographicemulsions in-whichi the solvent medium is predominantly organic areformed by dispersingin an or'ganic solvent =m=edium a complex formedby-precipitating gelatin from its aqueous dispersioncontaining silverhalide in suspensiongby means of a sulplionic acid containing a highly"hydrophobic radicle m the anion, thesaid aqueous --dispersion being" at:a pH valuev below the isoelectricpoi'nt cf th'e gelatin; Theprecipitated complex may-- contain a -smallproportion of water and-thisbe "includedinthe organicsolventdispersion. According to a furtherfeature of the inven-l tion, there is included ina photographicemulsionso formed a proportion of -anothercolloid-which is soluble in thesolvent medium already present i in the emulsion, or; which is solubl'ein' a solvent medium which --is miscible with' the solvent mediumalready present'in the emulsiong to f orr'n a stable combination. 1

Thegelatin/sulph'onate complexes containing silver halide may be'p'repar'ed-by the addition of the sulphonic acid or sulphonatesolutionto the gelatin silver halide'emuls-ion and allowing the gelatin complexto-sedimei'lit"outr The complexes may be redispersed {in the organicsolvent medium without 'wash'ing;'butit-is preferred'to-vvash thecomplex to'remov'e un antecl i'ons'; -Instead of the sulphonicacidits'el- --it is preferred to use the corresponding solublesaltsowingto-the rela tive insolubility of the 'free aciidsf 51 Thequantity ofsulphonic acidor sulphonate employed relative to fthegelatin'm'ayvaryf'but there is no advantage to be gaind'by using a quantitygreater than the stoich' iometric 'equi-va lent, i. e. about 10 rn gm.moles per gram of dry gelatin. f

For emulsion-making it is generallydesirable that the precipitatedgelatin/sulphonate; complex shouldbe soluble in water-miscible solventssince the precipitated complex invariably contains water, anditisdifficult to remove this water without adversely afiecting thequality ot'the emulsion. To this end it-* isfgenerally" desirable totreat the emulsion at a pH below the isoelectric pointof' the gelatinand in the presence of as little-electrolyteas'possible:

gsgs riall any sulphoniea'cid 0f1WhiCh-the alkali or am monium salt issoluble in water and of whichv the anion is highly hydrophobic maylie-employed. These maybe simpleacids, forexample naphthalene2-sulphonicacid; naphthalene 1.5- disulphonic it acid, naphthalene1-:3t5'-tri-sulphonic= acid; Z-naphthol-I -sulphonic acid;2"+naphthole-;

6 sulphonic acid} l-naphthol-a-sulphonic acid,,

tains a sulphoaryl-pyrazolone radicle; Naph thalene Orange GS .(ImperiaLChemical Indus-v tries Ltd-. and Tartrazine.

In general-it is'preferred to form: thecomplex from amaqueousgelatino-silverhalide. emulsion whiehhas alreadybeen washed anddigested;

Generally speaking the: most suitable organic solvents J for dispersingthe complexes are those containing hydroxy groups, e. g} methyl andethyl alcohols, ethylene glycol mono methyl ether; ethyl lactate anddiaceto ne alcohol. Organic solvents not containing hydroxy groupsaregenerally only useful together withfsojme water, ci some hy'droxy so1vee, g. acetone, meth l ethyl letone; di-

\ methylenefchloride, chloroform' and p i eb s" s admixture U methylalcohol. Srnallquantities Qt ers th l ac te Wy acme etherfs e. g..diethyl ether, .andfhydrocarbonse g, benzene and toluene, may-also beincluded in the lven m dium- The c oice (i b t l pend; on the particularnature of the complex; Solubility in, toluene and; chloroform appears toncr a e th sre tea h u nt we s phonate lative gelatin. Thecomplexesrfnay be; svvollen; in; the organic solvent 11 medium anddispersion is usually facilitated by gentlei warmmg. l r a The followingtable showsaexamples of the preferred conditionsfor -precipitatingagelatin/sul'phonate complex using-various sodium sulphornatcs.

tSolubility; clliaracl 4 ifi i flfi PE? I g gg cipitated complexSulphomc.Acl l d umsal l j 0 8, n: A

, queous Toluene 141001101;

. V Grams (iz) naphthalene-2-sulphonic acid 2.3 s ,vs (b) naphthalene1.5 disulphonic acid 1.61 v s, vs (0) naphthalene 1.3.5 trisulphonic '21id. 1.44:. 1 55 (d ZnaphthobG-sulphomc ac d s (e) l-naphthol b s (f)Tartrazine nq -l.102:0- i vs s=solub1e; vs==very soluble; ss slightly,solublcyiaingoluble;

Referring to this table, complex (a) in solution in aqueous alcohol isnot precipitated by the addition of excess alcohol and this complex isalso very soluble in carbon tetrachloride, acetone and ethyl acetate.Complex (1)) in solution in aqueous alcohol is precipitated by theaddition of excess alcohol and this complex is also soluble in ethylacetate and very soluble in acetone; the same remarks apply tocomplexComplex (e) in solution in aqueous alcohol is .precipitated by excessalcohol, and complex (1) in solution in aqueous alcohol is precipitated'by the addition of excess water.

In the preparation of the complexes referred to in this table thegelatin concentration was 0.5% and the temperature was 35 C. in eachcase.

As already indicated, an important feature of this invention is theformation of photographic emulsions which comprise a gelatin/sulphonatecomplex, containing silver halide, dispersed in an organic solventmedium, together with a proportion of another colloid soluble in suchorganic solventmedium or in an organic solvent medium miscibletherewith. Such other colloids may be, forv example, cellulose esters,e. g. cellulose nitrate, cellulose acetate, far-hydrolysedv celluloseesters (e. g. cellulose acetate having an acetyl content of to;%),polyvinyl acetates, polyvinyl acetals, methyl methacrylate polymers andthe partial hydrolysis products thereof, alkyd resins, and mixedinterpolymers suchas the interpolymers of maleic acid or anhydride withstyrene or methyl methacrylate.

The-following examples illustrate the invention, but are not to beregarded as limiting it in a y YZ Example I 1 1000 cc. of an aqueousgelatino silver bromid emulsion' contalning 11% gelatin and 17% silverbromide wasbrought to pH 2.0-2.4 by addition of 10 cc. concentratedhydrochloric acid. To this was added 400 cc. of an 8% solution in waterof sodium 2-naphthalene monosulphonate. The gelatin/sulphonate complex(containing suspended silver bromide) separated as a stiff oily complex.The supernatant liquid was decanted and the complex-dissolved in warmmethyl alcohol to form a 7% solution. This was a satisfactoryphotographic emulsion and could be coated in the usual way. Itssensitometric characteristies were substantially the same as those ofthe original aqueous gelatin it was obtained.

Example II To a photographic emulsion in methyl alcohol obtained inExample I wasadded, in turn:

Ethylene glycol mono-methyl ether 'cc 400 Low viscosity cellulosenitrate (10% solution ...in methyl alcohol) cc 300 Acetone cc 400 theneed for any special substratum or anchoring l,

layer since it adhered strongly to the lacquer coating both in the drycondition and during all stages of processing. The emulsion developednormally, and it was found that the coating was not melted by hot water.

Although in the above Example I the precipitated complex wasre-dispersed in methyl alcohol to form an emulsion for coating, otherwatervmiscible solvents may be used, for example ethyl emulsion fromwhich alcohol and ethylene glycol monomethyl ether.

The silver halide emulsions of this invention may contain any of theusual additions to silver halide emulsions, e. g. optical sensitisingdyes, sulphur sensitisers as for instance allyl isothiocyanate,goldsalts as described in U. S. P. 2,399,- 083, stabilisers,anti-fogging agents, toning agents and other agents for modifying thespeed, contrast, graininess, fog level and image colour of the products.

The invention provides photographic emulsions having a gelatin basisdispersed in organic solvent and the emulsions are therefore of value ina number of special applications. As already indicated they are ofparticular value for spray coating. Normal gelatin silver halideemulsions present considerable difficulties in spray coating since it isusually necessary to maintain the emulsion warm in the spray-gun toprevent it setting therein. Moreover, the ordinary emulsions will notadhere firmly if sprayed on to lacquered metal sheet. Emulsions may beprepared according to this invention, however, which have littletendency to set in the spray-gun. Moreover, the organic solvent usuallyhas a slight solvent action on lacquered surfaces and thus facilitatesadhesion between such surfaces and the emulsion sprayed thereon.

The spray-coating of lacquered metal sheets with photographic emulsionis of particular value in the production of photo-templates. In thecommercial application of this process, however, the users generallyprefer that the emulsion should be supplied in dry granular condition sothat it maybe re-dispersed when required to form an emulsion suitablefor spraying. The present emulsions are especially suitable in thisconnection. Emulsions prepared in organic solvent media according tothis invention can easily be derived by the Well-known expedlents offilm drying, spray drying, and air drying of the emul- I sion in theform of a shredded set jelly, since the organic solvent readilyevaporates. A further method is to precipitate the emulsion by adding itto water and, after breaking up the precipitate, to air-dry the product.

The emulsions of this invention, either as originally prepared or asre-constituted after drying, canbe used in any process wherespray-coating is required. The production of photo-templates has alreadybeen mentioned, and another useful application is in the preparation ofdials, nameplates and the like on metal or other surfaces. A furtherapplication is in the preparation of silk-screen printing surfaces. Inthis application the emulsion is sprayed on to stretched silk, dried,exposed, developed in a tanning developer and washed in hot water toproduce a wash-out reliefimage. It is a peculiar characteristic of theemulsions of this invention that, though quite insoluble in water whencoated, they tend to become soluble when allowed to stand in contactwith alkali, as in normal development, though the emulsions are stillnot soluble in water except at high temperatures. Fixing in an acidfixing bath, however, restores the insolubility of the complex even inhot water. Thus a suitable technique for using the emulsions in theproduction of silk-screen relief images is to develop the exposed imagein alkaline pyrocatechol, plunge the silk into hot water and then to fixthe wash-out relief image. An alternative technique is to prepare thewash-out relief image on a support from which it may be stripped and totransfer the image to a silk support.

The emulsions of this invention are also of value in colour photography.Thus they may contain dyes or dye-intermediates, e. g. colourformerswhich react with the oxidation products of aromatic primary aminodeveloping agents to form quinone-imine or azo-methine dyes, thecolour-former being uniformly dispersed in the emulsion. Thecolour-former, especially where particulate or of very high molecularweight, may be included in the original emulsion and precipitated withthecomplex, or it may be added to the final emulsion. Many of thehigh-molecular weight colour-formers, which are preferred from thestandpoint of being non-diffusing in the emulsion, are difi'lcult todisperse in ordinary aqueous gelatin silver halide emulsions, but moreeasily dispersed in the organic solvent emulsions of this invention. 7

The emulsions of this invention are permeable to ordinary alkalinedevelopers, but the degree of permeability depends on the preciseconstitution of the emulsion. By a suitable selection of an additionalcolloid, e. g. cellulose nitrate or a hydrophobic acid colloid,emulsions of varying degree of developer-permeability may be made, andaccordingly it is possible to build up a multilayer photographicmaterial for colour photography in which the several layers havedifferent degrees of permeability to ordinary developers and, byadjusting the constitution of the developers, e. g. by adding organicsolvents, to develop each of the layers separately. In such a process,by using aromatic primary amino developing agents containing differentcolour-formers, images in different colours may be formed in the variouslayers, and by a suitable selection of colour-formers a finaltrue-colour image may be obtained.

Another use to which the emulsions of this invention may be put is inthe production of printing paper to be used for printing from wetnegatives. As already stated the emulsions of this invention have a goodresistance to water, though they are readily developed by ordinaryalkaline developing solutions. Paper coated with emulsion according tothis invention may be used for printing from wet negatives, though it isusually desirable to employ an emulsion containing a proportion of othercolloids, e. g. cellulose nitrate and a methyl methacrylate-methacrylicacid co-polymer. Such emulsions not only have "a good resistance towater but also a good resistance to hypo, which may be carried bv thewet negative. Advantageously, in the production of wet-printing paperusing the emulsions of this invention the emulsion should be supercoatedwith a layerof a plain gelatin/anion soap complex in organic solvent, asdescribed in our copending application Serial No. 623,446, or a plaingelatin/sulphonate complex in organic solvent as described in co-pendingapplication Serial No. 84,485, filed March 30, 1949, which is acontinuation-in-part of application No. 623,446.

What we claim is:

1.. A photographic emulsion containing a complex of gelatin and asulphonic acid containing a highly hydrophobic radicle in the anion,said complex being soluble in a solution composed of methyl alcohol andcontaining dispersed silver halide, dispersed in a predominantly organicsolvent medium.

2. A photographic emulsion containing a complex of gelatin and asulphonic acid containing a highly hydrophobic radiole in the anion,said complex being soluble in a solution composed of methyl alcohol andcontaining dispersed silver halide, dispersed in a predominantly organicsolvent medium, said emulsion further containing a proportion of anothercolloid which is soluble in the said solvent medium.

3. A photographic emulsion containing a complex of gelatin and asulphonic acid containing a highly hydrophobic radicle in the anion,said complex being soluble in a solution composed of methyl alcohol andcontaining dispersed silver halide, dispersed in a predominantly organicsolvent medium containing methyl alcohol.

4. A photographic emulsion containing a complex of gelatin and asulphonic acid containing a highly hydrophobic radicle in the anion,said complex being soluble in a solution composed of methyl alcohol andcontaining dispersed silver halide, dispersed in a predominantly organicsolvent medium containing methyl alcohol and acetone, said emulsionfurther containing a proportion of another colloid which is soluble inthe said solvent medium.

5. A photographic emulsion containing a complex of gelatin and anaphthalene mono sulphonic acid, said complex being soluble in asolution composed of methyl alcohol and containing dispersed silverhalide, dispersed in a predominantly organic solvent medium.

6. A photographic emulsion containing a complex of gelatin and anaphthalene mono sulphonic acid, said complex being soluble in asolution composed of methyl alcohol and containing dispersed silverhalide, dispersed in a predominantly organic solvent medium, saidemulsion further containing a proportion of another colloid which issoluble in the said solvent medium.

7. A photographic emulsion containing a complex of gelatin and anaphthalene mono sulphonic acid, said complex being soluble in asolution composed of methyl alcohol and containing dispersed silverhalide, dispersed in a predominantly organic solvent medium containingmethyl alcohol.

8. A photographic emulsion containing a complex of gelatin and anaphthalene mono sulphonic acid, said complex being soluble in asolution composed of methyl alcohol and containing dispersed silverhalide, dispersed in a predominantly organic solvent medium containingmethyl alcohol and acetone, said emulsion further containing aproportion of another colloid which is soluble in the said solventmedium.

JOHN ALFRED HENRY HART.

KENNETH GEORGE ALFRED PANKHURST.

ROBERT CHARLES MORRIS SMITH.

REFERENCES CITED The following references are of record in the:

file of this patent:

UNITED STATES PATENTS

1. A PHOTOGRAPHIC EMULSION CONTAINING A COMPLEX OF GELATIN AND ASULPHONIC ACID CONTAINGIN A HIGHLY HYDROPHOBIC RADICLE IN THE ANION,SAID COMPLEX BEING SOLUBLE IN A SOLUTION COMPOSED OF METHYL ALCOHOL ANDCONTAINING DISPERSED SILVER HALIDE, DISPERSED IN A PREDOMINANTLY ORGANICSOLVENT MEDIUM.